Method and device for temper-hardening flat metal products

ABSTRACT

The invention discloses a method for temper hardening flat metal products, comprising the following steps: 
     introducing a flat product coming out of the furnace into a temper-hardening bay, depositing this flat product on supporting elements forming a lower substantially horizontal supporting table, causing a sudden cooling of the flat product in the deposited position, by spraying a temper-hardening liquid simultaneously on the whole of its upper surface and on the whole of its lower surface, removing the flat product from the temper-hardening bay, and further, before the sudden cooling, transferring retaining elements forming together a substantially horizontal retaining table to a horizontal retaining plane at a predetermined distance above the upper surface of the flat product and, during the sudden cooling, optionally retaining the flat product on the upper retaining table, within the limits imposed by the said horizontal plane. The invention also discloses a device for implementing this method.

This application is the national phase of international applicationPCT/BE97/00074 filed Jul. 1, 1997 which designated the U.S.

The present invention relates to a process for tempering flat metallicproducts comprising

an introduction of a flat product exiting from a furnace into atempering station with an upper surface orientated upwardly and a lowersurface orientated downwardly,

a location of the flat product on support elements forming together asubstantially horizontal lower support table of the tempering station,

a sudden cooling of the flat product in the located position, byspraying a tempering liquid simultaneously on all its upper and lowersurfaces, and

a removal of the cooled flat product from the tempering station, and toa tempering apparatus for the implementation of such a process.

Tempering processes of this type, intended to temper flat metallicproducts, such as sheets, strips and similar products, have been knownfor a long time. They are batch processes in which an upper pressingtable is lowered on the flat product to be tempered and is eitherpressed or placed down on it. The apparatuses implementing this type ofprocess are called tempering presses.

These processes enable the simultaneous spraying of the whole upper andlower surfaces of the flat product exiting out of the furnace with atempering liquid, for example water. However, they have the majordrawback of producing scratches on the surface of the tempered sheets.In effect, at the time of tempering, the sheets are subjected to asudden shrinkage whilst they are gripped between support elements of theupper and lower tables in the shape of fingers. Another drawback is thefact that at the time of tempering, the forward portion of the sheetexhibits a difference in temperature relative to the rear portion whichhas just exited from the furnace. The stresses caused by tempering arenot therefore uniform over the whole surface of the tempered sheets.

Continuous tempering processes are also known in which the sheets aretempered progressively as they exit from the furnace. Each portion ofthe sheet is therefore always cooled under the same conditions. However,such a sheet exhibits with this process enormous differences intemperature between a portion already tempered and one which has exitedfrom the furnace but is not yet tempered. These differences lead tostresses and deformations in the sheets, to such an extent that thistype of process has been virtually abandoned, especially for largesheets (see on this subject patents FR-1415912, U.S. Pat. No. 3,423,254,U.S. Pat. No 3,420,083, NL-135696, BE-A-758799, BE-A-789130 and U.S.Pat. No. 4,149,703).

The object of the present invention is to provide a batch temperingprocess and apparatus which does not appreciably exhibit the majordrawbacks described above. In particular it has for its object to allowtempering or hyper-tempering of fine flat products, for examplestainless steel sheets with a thickness of 3 to 30 mm, or carbon steelsheets with a thickness of 3 to 10 mm, to produce flat sheets which aresubstantially without scratches.

To solve this problem according to the invention, a process is providedsimilar to the one described above which comprises, before the suddencooling, a transference of retaining elements, which form together asubstantially horizontal upper holding table, into a horizontalretaining plane located a predetermined distance above the upper surfaceof the flat product, and during sudden cooling a possible retention ofthe flat product by the upper retaining table in the limits imposed bythe said horizontal retaining plane. This process, therefore, is nolonger tempering under compression and thus no longer has the drawbacksof the latter. On the contrary, the advantages of a simultaneous anduniform spraying on the whole of the upper surface and the whole of thelower surface of the sheet to be cooled are retained.

Advantageously, the above mentioned retaining plane is located at adistance of the order of 0.5 to 2.5 mm from the upper surface of theflat product to be tempered, preferably of the order of 0.8 to 1.2 mm,in particular of 1 mm.

In one embodiment of the invention the transference comprises acomprises a continuous measurement of the position of the retainingtable in relation to a fixed reference and a stoppage of thetransference when the said measurement reaches a predetermined value, inwhich the retaining table is located at the said predetermined distance.It is thus possible to allow the tempering of sheets with differentthicknesses, varying correspondingly the said predetermined value inrelation to the thickness of the sheet to be tempered.

In an advantageous embodiment of the invention, the transferencecomprises a continuous measurement of the position of the retainingtable, in several places, in relation to a fixed reference, a taking ofthe mean of these measurements, a calculation of the divergence betweeneach one of these measurements and the mean, a differential control ofthe transference of each of said places according to the calculatedcorresponding divergence, and a stoppage of the transference when thesaid mean reaches a predetermined value, in which the retaining table islocated at the said predetermined distance. It is thus possible toensure in a completely perfect manner the horizontal orientation of theupper table and a completely reliable retaining plane.

In a perfected embodiment of the invention, the tempering liquid isprovided from sources of tempering liquid arranged above and beneath theflat product to be cooled and in that the process comprises a relativedisplacement between sources of the tempering liquid and the flatproduct to be cooled. Thus it becomes possible to eliminate the coolingheterogeneities from one portion of the sheet to another, resulting fromthe fact that the sources of tempering liquid and the sheet are fixedone in relation to the other. Advantageously, the sheet is subjected toa horizontal displacement, in particular following a to-and-fromovement.

Other embodiments of the invention are indicated in the detaileddescription which follows.

The invention also relates to a tempering apparatus for flat metallicproducts comprising

means for introducing a flat product exiting from a furnace into theapparatus with an upper surface directed upwardly and a lower surfacedirected downwardly,

support elements forming a lower support table on which the introducedflat product is placed in a substantially horizontal position,

means for sudden cooling of the flat product in the located positionwhich submit it to a spray of tempering liquid simultaneously over allof its upper surface and all of its lower surface, and

means for removal of the cooled flat product from the temperingapparatus.

According to the invention, the apparatus comprises

retaining elements forming together a substantially horizontal upperholding table,

transference means capable of conveying the retaining elements above theupper surface of the flat product, and

control means for the transference means capable of controlling thetransference means and of stopping them when the retaining elements arein a horizontal retaining plane located a predetermined distance abovethe upper surface of the flat product to be tempered.

Other details and distinctive features of the invention will bedescribed in the following description, as a non-limiting example andwith reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic front view of a tempering apparatusaccording to the invention.

FIG. 2 shows a diagrammatic plan view of the apparatus shown in FIG. 1.

FIG. 3 shows a block diagram of a control unit for apparatus accordingto the invention.

FIG. 4 shows a detail of an upper table of the apparatus shown in FIG.1.

In the various drawings, identical or equivalent elements are designatedwith the same references.

As illustrated by the embodiments shown in FIGS. 1 and 2, the apparatuscomprises a series of gantries made of two columns 1 and 2 and two fixedcrosspieces 3 and 4. The lower fixed crosspieces 4 support throughlongitudinal girders 6, a lower table 5 which in the illustrated exampleis fixed. This table 5 is formed by parallel beams 7 spaced from oneanother. These beams themselves support, in a manner not shown, knownsupport elements, for example in the shape of claws. The latter can, forexample, take the shape of the retaining elements shown in FIG. 4, in aninverted position.

On the upper side, an upper table 9, similar to the lower table isattached to movable beams 10 via longitudinal girders 11. The movablebeams 10 are fitted with end blocks 12 and 13 able to slide on guides 14and 15 fitted on columns 1 and 2. In the case illustrated, each one ofthe movable beams 10 is supported by two hydraulic rams 16 and 17.

In a similar way to lower table 5, the upper table 9 is made of parallelspaced beams 18. Retaining elements are suspended, according to theinvention, from these beams and in this example can be holding claws 8such as those shown in FIG. 4.

The means of introducing the sheet 31 to be tempered is a knowntechnique and is therefore not shown. There is provided between the exitfrom the reheating furnace and the entrance to the tempering apparatusparallel rollers turning on their axis in order to drive the sheethorizontally, that is to say with an upper surface orientated upwardlyand an lower surface orientated downwardly (see for exampleFR-14115912). Inside the tempering apparatus, identical rollers aremounted on a framework which can be, in a known manner, lifted andlowered. During the entry of the sheet, the framework is lifted and therollers move the sheet. When the sheet is completely inside theapparatus, the framework is lowered and the rollers are retractedbetween the beams 7 of the lower table. Such an arrangement is providedin the known tempering presses, notably in those marketed by MessrsDREVER CY. It has therefore not been shown in detail in the drawings.Similarly, the means for removal of a cooled flat product from thetempering apparatus are similar rollers, known to specialists, and whichare therefore not shown or described in greater detail here. The suddencooling means of the flat product to be tempered are, in the exampleillustrated in FIG. 4, perforated pipes 19 fed with pressurizedtempering liquid, notably water. Such pipes, known to specialists, arelaid out above and under the sheet to be cooled in order to be able tospray its upper and lower surfaces in a manner as uniform as possible.The supply means for these pipes are not shown as they are widely knownto specialists.

The tempering apparatus according to the invention comprises a transfermeans for the upper table 9, which in the illustrated case, arehydraulic rams 16 and 17. It should be noted that a table, such at thatillustrated, weighs approximately fifty tonnes. As it is mainly made oflongitudinal and transverse beams, it does not have a very greatrigidity. Consequently, it is necessary to guide the rams precisely toconvey the end of the fingers 20 of the retaining claws 8 into ahorizontal plane located at a predetermined distance from the sheet tobe tempered. Ram 17 of FIG. 1 is a "master" ram which is fitted with anintegrated or external position coder which allows continuousmeasurement of the position of the table at any position in relation toa fixed reference. In FIG. 3, can be seen such a position coderconsisting of a measuring scale 21 mounted on a fixed crosspiece 3 and ameasurement reader 22 mounted on a lower table 9, at the foot of masterram 17. Ram 16 in FIG. 1 is guided simultaneously with ram 17, but is aslave to the movement, that is to say to the output produced by theintroduced pressurizing fluid.

In FIG. 2, one can see in this embodiment four master rams 17 locatedalternatively on the left and on the right of the tempering apparatus inorder to ensure the accuracy of the upper table along all of its length.Thus, as illustrated in FIG. 3, the tempering apparatus comprises ahydraulic unit 23 intended to feed the rams with pressurized medium,this unit also controls the support framework of the sheet carryingrollers and allows its ascent and descent.

Hydraulic unit 23 comprises, for example, proportional valves, stopvalves and flow dividers. These valves and dividers are in a numbercorresponding to the number of gantries of the device. The flow dividersensure a distribution of the flow of pressurized medium between the leftand right rams of the same gantry. The proportional valve regulates theoutput produced by the ram as a function of the position indicated bythe position coder linked to the master ram 17. The stop valves arrestthe upper table when it attains the required position.

The hydraulic unit 23 is controlled by control means. These controlmeans comprise the position coder 21, 22 which continuously transmitsits readings to a comparator 24. This comparator receives from aprogrammable means 25 a predetermined set-point value and compares itwith the measurements received from the position coder. The divergencescalculated by comparator 24 is transmitted to a position regulator 29which may comprise control cards, with one card for each gantrycontrolling a master ram 17. According to the signals received, asdescribed below in greater detail, the card controls the proportionalvalves and the stop valves of the hydraulic unit 23. The programmablemeans receives information and instructions from a computer monitoringsystem 26, itself connected to a works management computer system 27.

The operation of the tempering apparatus according to the invention willnow be described.

Flat products to be tempered, especially sheet metal, exit continuouslyfrom a reheating furnace onto a roller table and are immediatelyintroduced on to the rollers supported by the framework of a temperingapparatus. When the sheet is completely inside the latter, the frameworkis lowered and the rollers are retracted between beams 7 of the lowertable of the tempering apparatus.

The sheet is thus located on the support elements, which in this casecan for example be known support claws, provided with upwardly directedfingers.

During the introduction and the positioning of the sheet, the pistons ofthe rams 16 and 17 are in their retracted positions and the upper table9 is in its high position.

It is afterwards lowered in a controlled matter until retaining elements8 in the shape, for example, of retaining claws provided with downwardlydirected fingers 20 are located on a retaining horizontal plane situatedat a very small predetermined distance from the upper surface of thesheet (see FIGS. 1 and 3).

The computer monitoring system 26 is informed about the sheets whichwill be tempered according to the encoding of their identification on aterminal not shown which is, at 28, connected to system 26. System 26then interrogates the works computer system 27 to ascertain thecharacteristics of this product, namely, in particular the thickness ofthe sheet to be tempered. On the basis of this information, system 26transmits the thickness and the optimal tolerance (distance 30 betweenthe sheet and the retaining elements 8 in the lowered position of table9) to programmable means 25 which manages the whole of the temperingprocess sequences. These sequences are especially those which relate tothe ascent and the descent of the framework carrying the rollers, theentry and exit movements of the sheet in and out of the apparatus andthe movement of the upper table.

For this last mentioned movement, programmable means 25 transmits tocomparator 24 a predetermined set-point value in which the retainingelements 8 are at the said predetermined optimal distance 30. Comparator24 compares this value with the mean of the values continuouslytransmitted by the position coders associated with master rams 17. Italso compares each measurement received from the position coders withthis mean and thus determines different divergences. The divergences arethen transmitted to regulator 29 which correspondingly commands thevalves of the hydraulic unit 23. As a control card is allotted to eachmaster ram 17, it is possible to regulate the movement of upper table 9towards the lower position in different ways here and there by spotcontrol in order to obtain a perfectly plane and horizontal position oftable 9 at the lowest point. In this position, comparator 24 comparesthe said mean of the measurements with the set-point value, notes thatthere is no longer a divergence and transmits a stop signal to theregulator.

Preferably, the distance 30 will be of the order of mm or less. In thisway, the retaining elements 8 do not touch the upper surface of thesheet.

One then proceeds with the tempering or hyper-tempering of the sheet.Programmable means 25 control the feed of the tempering liquid underpressure to pipes 19 which spread it as uniformly as possible on theupper and lower surfaces of the sheet.

During this sudden cooling, the sheet can thus shrink without beinggripped between the upper and the lower tables. The stress problemswhich result in the sheet and the appearance of scratches on the surfacelargely disappear. If, during this shrinkage, a sheet becomes slightlydeformed, the distance 30 is calculated to retain this product withinthe limits of the horizontal holding plane formed by fingers 20 of theretaining elements 8 within limits which are acceptable in the process.Thus one avoids the cooling heterogeneities, which without this holdingplane will result in the formation of channels for the tempering liquidcaused by the deformation of the sheet.

After tempering the roller table is lifted and the sheet exits from thetempering apparatus.

One thus obtains sheets which have not been subjected to practically anystress during the cooling process. Contrary to what was the generalopinion according to the previous methods, the treated sheets accordingto the invention are not subjected to temper rolling during cooling and,on the contrary, the sheets are "liberated" to avoid the formation ofinternal stresses during tempering. As tempering is, according to theinvention, carried out in the most uniform manner possible, there ispractically no stress in the sheet, and this without pressing, and thereare no longer any scratches, at least on the upper surface of thesheets.

The scratches that occasionally form on the lower surface are reduced toa minimum because, especially in the case of thin sheets, the contactpressure between the retaining elements and the sheet is very small andcorresponds only to the weight of the sheet.

It should be understood that this invention is in no way limited to theembodiment described above and that many modifications can be madewithout falling outside the scope of the attached claims.

One can, for example, imagine that the support elements of the lowertable and the retaining elements of the upper table are not claws butrather rollers, for example like those used in the apparatus forcontinuous tempering (see especially U.S. Pat. No. 3,423,254). Theserollers can be stopped once the sheet is entirely within the temperingapparatus. Advantageously, these rollers can be ribbed or grooved,possibly in spiral fashion (see for example U.S. Pat. No. 3,420,083 andU.S. Pat. No. 4,149,703).

One can also imagine that once the sheet is completely within thetempering apparatus, these rollers can be rotated, for example followinga to-and-fro movement. This causes an oscillating movement of the sheetin relation to pipes 19 and therefore a better distribution of thetempering liquid on the sheet surfaces during the process and thiswithout contact of the sheet with the upper table.

One can also cause a displacement of the spraying system in relation tothe sheet, for instance by mounting spraying ramps on a movableoscillating framework controlled by a link/crank device. A rotation ofthe spraying ramps about their axes can also be provided.

One could also provide retaining and support elements in the shape ofrollers or balls. The front face of the fingers of the holding elementsand the support elements in the shape of claws could also be grooved orchamfered or have a hemispherical profile.

What is claimed is:
 1. Tempering process for flat metal productscomprisingan introduction of a flat product exiting from a furnace intoa tempering station with an upper surface oriented upwardly and a lowersurface oriented downwardly, a location of the flat product on supportelements forming together a substantially horizontal lower support tableof the tempering station, a sudden cooling of the flat product in thelocated position by spraying a tempering liquid simultaneously on allits upper and lower surfaces, anda removal of the cooled flat productfrom the tempering station, as well as before the sudden cooling, atransference of retaining elements forming together a horizontal upperretaining table towards the upper surface of the flat product to betempered, and comprising a stoppage of the transference withimmobilization of the retaining elements in a horizontal retaining planelocated at a distance from the upper surface of the flat product, andduring the sudden cooling, a retention of the flat product byimmobilized retaining elements, only when the flat product has atendency to deform outside the limits imposed by the said horizontalretaining plane.
 2. Process according to claim 1, characterized in thatthe said retaining plane is located at a distance of about 0.5 to 2.5 mmfrom the upper surface of the flat product to be tempered.
 3. Processaccording to claim 1, wherein the transference comprises a continuousmeasurement of the position of the retaining table in relation to afixed reference and there is a stoppage of the transference when thesaid measurement reaches a value, in which the retaining table islocated at the said distance.
 4. Process according to claim 1, whereinthe transference comprises a continuous measurement of the position ofthe retaining table, in several places, in relation to a fixedreference, a taking of the mean of these measurements, a calculation ofthe divergence between each one of these measurements and the mean, adifferential control of the transference of each of said placesaccording to the calculated corresponding divergence and a stoppage ofthe transference when the said mean reaches a value, in which theretaining table is located at the said distance.
 5. Process according toclaim 1, wherein the tempering liquid is provided from sources oftempering liquid arranged above and beneath the flat product to becooled and in that the process comprises a relative displacement betweensources of the tempering liquid and the flat product to be cooled. 6.Process according to claim 1 wherein, during the sudden cooling, theflat product is stationary.
 7. Process according to any one of the claim1 wherein, during the sudden cooling, the flat product is subjected to ahorizontal displacement following a to-and-fro movement.
 8. Temperingapparatus for flat metallic products comprisingmeans for introducing aflat product exiting from a furnace into the apparatus with an uppersurface directed upwardly and a lower surface directed downwardlysupport elements forming a lower support table on which the introducedflat product is placed in a substantially horizontal position, retainingelements forming together a substantially horizontal upper holding tabletransference means capable of conveying the retaining elements above theupper surface of the flat product, means for sudden cooling (19) of theflat product in the located position which submit it to a spray oftempering liquid simultaneously over all of its upper surface and all ofits lower surface, and means for removal of the cooled flat product fromthe tempering apparatus comprisingcontrol means for the transferencemeans capable of controlling the transference means and of stopping themto immobilize the retaining elements in a horizontal retaining planelocated a distance above the upper surface of the flat product to betempered, and in that during the sudden cooling the immobilizedretaining elements retain the product flat only when it has a tendencyto deform outside limits laid down by the said horizontal retainingplane.
 9. Apparatus according to claim 8, characterized wherein thecontrol means comprises at least one measurement reader whichcontinuously measures the position of the retaining table in relation toa fixed reference, a comparator which determines the presence or absenceof a divergence between the said measurements and a predetermined valuein which the retaining elements are at the said pre-determined distanceof the flat product to be tempered, and a position regulator acting onthe transference means as a function of the divergence.
 10. Apparatusaccording to claim 8 wherein the control means comprises a plurality ofmeasurements readers which each continuously measures the position of aparticular place on the retaining table in relation to a fixedreference, and wherein the comparator compares in addition thedivergence between each measurement and their mean, and wherein theposition regulator acts differently on each or some of the transferencemeans according to the predetermined divergences in each of theparticular places and stops the transference means when the comparatordetermines an absence of divergence between the said mean and the value.11. Apparatus according to claim 8 wherein the transference meanscomprise hydraulic ram connected between a fixed framework of theapparatus and the upper retaining table and fed by a hydraulic unitaccording to the signals received from the control means.
 12. Apparatusaccording to claim 8 wherein the retaining elements and the Supportelements are identical elements arranged symmetrically in relation to ahorizontal plane.
 13. Apparatus according to claim 8 wherein the supportelements and/or the retaining elements are claws, jaws, rollers withgrooves or with ribs or equivalent means which, when in contact with theflat element to be tempered, only cover a partial area of the latter.14. Apparatus according to claim 8 wherein the support elements arerollers which drive the flat element in a to-and-fro movement during thesudden cooling.
 15. Apparatus according to claim 8 wherein the suddencooling means comprises spraying pipes provided with an oscillatingmovement.
 16. Process according to claim 2 wherein the retaining planeis located at a distance of about 0.8 to 1.2 mm from the upper surfaceof the flat product to be tempered.
 17. Process according to claim 2wherein the retaining plane is located at a distance of about 1 mm fromthe upper surface of the flat product to be tempered.
 18. Apparatusaccording to claim 15 wherein said spraying pipes are driven in rotationabout their axes.